A man can row 9 km/h in still water. He rows to a place 24 km away and back in a total of 6 hours. Find the speed of the river current. MCQ with Answer and Explanation
A man can row 9 km/h in still water. He rows to a place 24 km away and back in a total of 6 hours. Find the speed of the river current.
A. 2 km/h
B. 3 km/h
C. 4 km/h
D. 5 km/h
Answer: Option B
Solution (By JKSSB Mock Tests)
Let speed of current be c. 24 / (9 + c) + 24 / (9 - c) = 6. Dividing by 6: 4 / (9 + c) + 4 / (9 - c) = 1 => 4(9 - c + 9 + c) = 81 - c^2 => 72 = 81 - c^2 => c^2 = 9 => c = 3 km/h.
Explanation:
Let the time duration be t hours. Difference in distance = 12t - 9t = 3t = 15 km => t = 5 hours. Actual distance traveled = 9 * 5 = 45 km.
A person can row 10 km/h in still water. If it takes him exactly twice as long to row upstream as to row downstream over the same stretch, find the speed of the current.
Explanation:
Let speed of current be c km/h. Downstream speed = 10 + c, Upstream speed = 10 - c. Given: 2 * (10 - c) = 10 + c => 20 - 2c = 10 + c => 3c = 10 => c = 10/3 = 3.33 km/h.
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